When 2 clinical strains of plasmid-mediated penicillin-resistant Staphylococcus aureus were treated with 1 mM sodium ascorbate for 6 h, 12-35% colony-forming units (CFU) irreversibly lost their ability to produce beta-lactamase. Agarose gel electrophoresis showed the disappearance of the plasmid bands from the lysates of colonies in which susceptibility to penicillin was induced by ascorbate treatment. Since ascorbic acid is a compound that is completely non-toxic, the possibility of its therapeutic use in the treatment of multiresistant bacterial diseases is proposed.